Mix the cream and sweetener together in a saucepan, and bring slowly to a boil, stirring frequently. Let it boil for about three minutes before removing from the heat.

Reserve a small amount of the zest for garnish, then add the remaining zest and juice to the cream. Stir well, and the mixture will start to thicken.

Leave to cool for five minutes, stirring occasionally, then transfer to serving glasses or dishes. Let it cool completely, then cover and store in the fridge until required.

To serve, sprinkle the lemon zest over each lemon posset.